Monolithic 3D Integration With Photosensor and CMOS Circuits Using Ion-Cut Layer Transfer

A thin Si layer transfer process for monolithic 3D (M3D) integration is proposed using hydrogen ion (H
⁺
) implantation. The upper Si layer was transferred to CMOS circuits fabricated on the lower substrate by H
⁺
implantation, oxide-to-oxide bonding, and a cleavage process at low temperature (< 500 °C). The M3D system comprising the photosensor connected to the CMOS device was demonstrated, where the thickness and roughness of the transferred Si layer were determined by H
⁺
implantation and subsequent processes. The hetero-junctional photosensor was fabricated on the transferred Si layer, which generated the photocurrent (
$\text{I}_{\text {ph}}$
) by light exposure. The photosensor and ring oscillator circuits of the vertical structure implemented by the M3D process generated the
$\text{I}_{\text {ph}}$
according to the light exposure intensity and showed different frequency behaviors accordingly. Compared with the continuous device scaling approach, M3D may be an alternative scheme for low-power, high-performance, and multi-functional devices.